Biotite
| Biotite | |
|---|---|
 Thin tabular biotite aggregate (Image width: 2.5 mm) | |
| General | |
| Category | Dark mica series |
| Formula (repeatin unit) | K(Mg,Fe) 3(AlSi 3O 10)(F,OH) 2 |
| Creestal seestem | Monoclinic (2/m) Space Group: C 2/m |
| Identification | |
| Formula mass | 433.53 g |
| Colour | Mirk broun, greenish-broun, blackish-broun, yellae, white |
| Creestal habit | Massive tae platy |
| Twinnin | Common on the [310], less common on the {001} |
| Cleavage | Perfect on the {001} |
| Fractur | Micaceous |
| Tenacity | Brickle tae souple, elastic |
| Mohs scale haurdness | 2.5–3.0 |
| Skinkle | Vitreous tae pearly |
| Streak | White |
| Diaphaneity | Skyre tae leamin tae opaque |
| Speceefic gravity | 2.7–3.1 |
| Density | 2.8–3.4 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.565–1.625 nβ = 1.605–1.675 nγ = 1.605–1.675 |
| Birefringence | δ = 0.03–0.07 |
| Pleochroism | Strong |
| Dispersion | r < v (Fe rich); r > v weak (Mg rich) |
| Ultraviolet fluorescence | None |
| References | [1][2][3] |
Biotite is a common phyllosilicate meeneral athin the mica group, wi the approximate chemical formula K(Mg,Fe)
3AlSi
3O
10(F,OH)
2. Mair generally, it refers tae the dark mica series, primarily a solid-solution series atween the iron-endmember annite, an the magnesium-endmember phlogopite; mair aluminous endmembers include siderophyllite. Biotite wis named bi J.F.L. Hausmann in 1847 in honour o the French pheesicist Jean-Baptiste Biot, who, in 1816, researched the optical properties o mica, discovering mony unique properties.[4]
Biotite is a sheet silicate. Airn, magnesium, aluminium, silicon, oxygen, an hydrogen furm sheets that are waikly boond thegither bi potassium ions. It is whiles cried "iron mica" acause it is mair airn-rich nor phlogopite. It is an aa whiles cried "black mica" as opponed tae "white mica" (muscovite) – baith furm in some rocks, in some instances side-bi-side.
References
- ↑ Biotite mineral information and data Mindat
- ↑ Biotite Mineral Data Webmineral
- ↑ Handbook of Mineralogy
- ↑ Johann Friedrich Ludwig Hausmann (1828). Handbuch der Mineralogie. Vandenhoeck und Ruprecht. p. 674. "Zur Bezeichnung des sogenannten einachsigen Glimmers ist hier der Name Biotit gewählt worden, um daran zu erinnern, daß Biot es war, der zuerst auf die optische Verschiedenheit der Glimmerarten aufmerksam machte." (For the designation of so-called uniaxial mica, the name "biotite" has been chosen in order to recall that it was Biot who first called attention to the optical differences between types of mica.)